Currently available solar heat collectors of the evacuated double-tubing type are similar to U.S. Pat. No. 2,460,482 or even U.S. Pat. No. 980,505. The currently available solar heat collectors typically include an outer straight glass tube being closed at one end and open at the other end, and an inner straight glass tube of a lesser diameter which is also closed at one end and open at the other end. Both tubes are hermetically sealed at their open ends, and the space therebetween is evacuated to a predetermined degree of vacuum. The inner tube is then provided over its outer surface with a solarheat absorbing film.
To make effective use of the collected solar heat, U.S. Pat. No. 3,952,724 teaches that a hairpin metal pipe for circulation of fluid media may be inserted into the above-mentioned collectors.
With this known arrangement, how the collected solar heat is transmitted to the metal pipe is of vital importance. However, to date, an ideal solution to such a problem has not yet been uncovered.